My practical experience with tuning a multiband dipole (where you have
separate elements for 40,20, and 10) is that folding the elements (or
wadding it up in a ball) is a great way to adjust it, because you can
shorten easily, and then lengthen again when you decide that you
overshortened.
As for adding capacitive loading.. it might, but it's probably not hugely
significant (you're basically increasing the effective diameter of the
wire). I doubt that the capacitive loading is enough to shorten the antenna
enough to make a difference in, for instance, the SWR bandwidth. You're
probably talking about a foot or two out of 40-50 feet, which isn't a huge
difference from the bandwidth/Q standpoint.
In any case, you're adjusting it by trimming, not calculation, right? so any
effects from the extra length just wind up changing the optimum tune point.
I assume that you'll leave it folded up forever, once you've found the
point? Or are you planning on cutting off the extra? If the latter, then,
you do have a problem, because, while the overall antenna performance won't
change much, the wire will change the resonant frequency.
Jim, W6RMK.
----- Original Message -----
From: "Ken Kinyon" <w7ts@comcast.net>
To: <TowerTalk@contesting.com>
Sent: Tuesday, November 30, 2004 10:06 AM
Subject: [TowerTalk] adjusting insulated wire dipole
> I am building a trapped inverted vee from insulated wire. I expect that
> there will a lot of length adjustment to be done on each segment before I
am
> happy with the center frequencies.
> My thought is to leave extra wire (still insulated) folded back along the
> length of the segment and clamp it. I seems to me that this should act
like
> capacitive end loading on each segment and increase the electrical length.
> Is this correct? Is the amount enough to be significant?
> Thanks,
> Ken W7TS
>
> -------------------
> Kenneth E. Kinyon
> 34 Princeton Circle
> Longmont, CO 80503-2106
> -----------------------
> E-mail: W7TS@comcast.net
> ------------------
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
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questions and ask for Sherman, W2FLA.
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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